Microparticles and their therapeutic or diagnostic use

ABSTRACT

Microcapsules having a wall thickness of no more than 500 nm, and a bulk density of no more than 0.2 g.cm −3 , are suitable for therapeutic or diagnostic use. They are aerodynamically light, and can be used for delivery to the lung, or diagnosis by ultrasound.

FIELD OF THE INVENTION

This invention relates to microparticles and their therapeutic ordiagnostic use. More particularly, the invention relates to the deliveryof an active agent to the lungs, by inhalation, and to diagnosticimaging using ultrasound.

BACKGROUND OF THE INVENTION

Edwards et al, Science 276: 1868-71 (1997), reports the production ofparticles of small mass density and large size, for use in pulmonarydrug delivery. The objective was to provide an insoluble matrix whichcould act as a reservoir for sustained drug release, analogous to asustained release tablet. Porous and non-porous particles were prepared,the porous particles being preferred for their “high efficiency”. The“particle mass density” values for these particles were about 0.1 g.cm⁻³and 0.8 g.cm⁻³, respectively. The porous particles apparently compriseda solid matrix including pores, the matrix being essentially a carrierfor a therapeutic agent (the given examples being testosterone andinsulin) held within the matrix.

Note 14 of Edwards et al states that the density is determined bynon-mercury porosimetry or tap density measurements. The latter at leastwould not give a true particle density. Reference 15 (French et al, J.Aerosol Sci. 27:769 (1996)) clearly shows bulk densities. Note 14 refersto Vidgren et al, Int. J. Pharm. 35:139 (1987), which uses an “effectivedensity”. Hence, little can be concluded as to the meaning of “particlemass density”.

WO 98/31346 apparently relates to products similar to those disclosed byEdwards et al. The particles are aerodynamically light, and generallyporous.

A difficulty with many sustained release inhalation therapies is thatsolid (or more dense) particles will be subject to clearance mechanismsand therefore unable to act as a reservoir. Any such particles landingin the trachea or bronchi will be rapidly removed by mucociliaryclearance mechanisms. Similarly, particles reaching the non-ciliatedregions of the deep lung are rapidly cleared by macrophage activity. Thematerial reported by Edwards et al is intended to avoid both theseproblems, by providing a particle of relatively large geometric diameter(>5 μm) which will avoid phagocytosis by macrophages, but which isaerodynamically small (i.e. a low density with respect to geometricdiameter), and which will reach the non-ciliated region of the deeplung. Sustained release is then achieved by use of an insoluble matrixof material.

The particles disclosed by Edwards et al. were prepared by double- andsingle-emulsion solvent evaporation techniques. It is also stated thatporous particles comprising therapeutics and pharmaceutical excipientscan easily be formed by spray-drying, and refers in this context to anarticle by Sacchetti and van Oort in “Inhalation Aerosols” (May 1996) AJ Hickey ed., Dekker N.Y. pub., pages 337-384. No specific indication isgiven as to how particles of low density might be obtained byspray-drying. For inhalation therapy, a dry powder must be dispersedinto an airstream as discrete particles, to ensure controlledreproducible administration of a standard dose. To achieve this, thepowder is usually loaded onto a carrier such as lactose, throughblending. The objective is to produce a blend in which the drug powderis distributed as discrete particles evenly over the carrier. If this isnot achieved, and the particles are agglomerates, there is an apparentincrease in aerodynamic size and a reduction in dosing efficiency.

While compounds that can be administered without carrier are known, e.g.sodium cromoglycate and terbutaline, these are usually either extremelysafe or relatively inactive, allowing therapeutic effects to be achievedas a result of the inefficient administration of enormous quantities ofmaterial. Moreover, the use of carriers can cause additional drugformulation difficulties. For example, lactose, the most commonly usedmaterial for this purpose, is a reducing sugar and can react chemicallywith some drug substances, such as proteins and peptides.

The mechanical manipulation of lactose, such as blending and sieving,also results in “high energy spots” on the surface of the carrier. Thisresults in a reduction of inhalation efficiency, because of theadditional energy required to disperse the drug material.

The use of spray-drying in pharmaceutical processing is not new.However, it is usually used to bind particles together, for the purposesof obtaining powders with good flow properties.

U.S. Pat. No. 5,202,159 describes spray-drying a slurry of diclofenac,excipients, methacrylic acid-ethyl acrylate copolymers and polyethyleneglycol, and formulating the product into tablets. U.S. Pat. No.4,971,787 discloses spray-drying a medicament with sugar, andformulating the product with a specific gum base, to give a chewing gumcomposition.

U.S. Pat. No. 4,180,593 discloses producing free-flowing blown bead foodproducts, by spray-drying the foodstuff with a blowing agent, and thenquenching, in order to control the bulk density. The reported bulkdensity in the only Example is about 0.1 g.cm⁻³ (6 lb/ft³).

SUMMARY OF THE INVENTION

By contrast to the prior use of spray-drying, for bonding particlestogether in a medicament, the present invention uses spray-drying forthe production of large, light particles. More particularly, it has nowbeen found that microcapsules having properties that are particularlysuitable for use in ultrasound diagnostic procedures, i.e. non-porous,and for the delivery of a therapeutic agent by inhalation, can beprepared by the simple expedient of including a blowing agent in theformulation to be spray-dried. As a result, microcapsules having a bulkdensity of no more than 0.2 g.cm⁻³ can be obtained.

Microcapsules of the invention are very suitable for formulation in aninhaler. If they comprise a therapeutic agent, they provide rapidrelease and subsequent uptake of drug in the lung, and avoid drugencapsulation, quite by contrast to any sustained release formulation.Further, products of this invention do not require a carrier, foreffective administration to the lung. An inhaler including microcapsulesof the invention may therefore contain the microcapsules as the sole orpredominant component of the inhalable formulation.

Thus, the present invention allows the controlled, reproducibleadministration of small quantities of potent and/or expensive medicineswithout the need for carrier material. Problems associated with the useof lactose can be avoided.

Moreover, if the microcapsules contain only wall-forming material, andno therapeutic agent is included as such, they are particularly suitablefor use in ultrasonic imaging. The relatively thin walls of themicrocapsules apparently provides improved echogenicity.

DESCRIPTION OF THE INVENTION

Procedures for preparing microparticles by spray-drying, suitablewall-forming materials (such as albumin), and processes for stabilisingthe microparticles, e.g. by heat or chemically, are fully described in,inter alia, WO 92/18164 and WO 96/15814 (describing the currentlypreferred process), the contents of which are incorporated herein byreference. According to the present invention, these procedures aremodified by the inclusion of a blowing agent, in the feedstock forspray-drying.

The blowing agent is a volatile substance which releases a gas or gasesduring the spray-drying process. Blowing agents are used in the presentinvention, to produce hollow microcapsules. Suitable blowing agentsinclude ammonium acetate, ammonium hydroxide, ammonium carbonate,ammonium bicarbonate, acetic acid, formic acid and hydrochloric acid.The pH at which these blowing agents are used may vary; this impliesthat compounds with pH-dependent solubilities can be spray-dried withthe addition of a suitable blowing agent.

By way of example, the blowing agent used in the production of albuminmicrocapsules is ammonium carbonate which releases ammonia, carbondioxide and water vapour. During spray-drying, these three gases expandin the atomised droplets, causing the droplet to increase in size, toproduce larger, thinner-walled microcapsules.

Products of the invention may have various characteristics, depending onthe conditions of their preparation. For example, their median size is 1to 20 μm, and their wall thickness is no more than 500 nm, e.g. 10 to250 nm, more preferably 100 to 150 nm. Their bulk density may be 0.01 to0.15 g.cm⁻³, more preferably 0.04 to 0.1 g.cm⁻³.

The microcapsules of the invention comprise a wall-forming material and,if desired, a therapeutic agent (which may be the same). If thewall-forming material and the therapeutic agent are different, themicrocapsules may be formed by co-spray-drying.

As indicated above, the microcapsules may comprise albumin, andpreferably human serum albumin. Albumin may be used as a therapeuticagent per se, or as a wall-forming material in combination with atherapeutic agent. Other active agents for use in the invention will bechosen having regard to the desired effect. Examples of active agentsthat may be used include cotranscytosis factors, fibrinogen, thrombin,insulin, growth hormone, calcitonin, α-antitrypsin, FSH, α-interferon,β-interferon, heparin, Factor VIII, Factor IX, interleukins and bloodcoagulation factors. Other wall-forming materials that may be used aredescribed in WO 92/18164.

For the preferred route of administration, the soluble microcapsulesobtained by spray-drying are used. As indicated above, stabilisation maybe used, if another route of administration is required and/or fordiagnostic purposes. The amount of microcapsules to be administered canreadily be determined by the skilled man.

The following Examples illustrate the invention.

EXAMPLE 1

212 ml diafiltered 10% w/w HSA solution containing 60 g ammoniumcarbonate was spray-dried on a standard Mobile Minor spray-dryer. Theconditions were as follows:

Inlet temperature − 220° C. Atomisation pressure − 2.0 barg Feed rate −21.4 g/min Atomisation type − 2-fluid nozzle Liquid insert − 0.5 mm

The non-fixed microcapsules obtained by spray-drying, which are soluble,behaved as a powder, demonstrating liquid fluidised properties. They aresuitable for use as such, in an inhaler.

For testing purposes, 4 g microcapsules obtained by spray-drying wereheat-stabilised for 55 minutes at 176° C. in a hot air oven. After heatstabilisation, the microcapsules retained their fluidized properties.

A 50 mg aliquot of heat-stabilised microcapsules was dispersed inde-ionised water (sonication in ethanol was not necessary). Thesuspension was then microscopically examined and sized using a CoulterCounter fitted with a 50 μm aperture tube.

Microscopic examination showed the presence of 2 distinct populations ofmicrocapsules. The first population consisted of hollow, air-containingmicrocapsules approx. 5 μm in size, and the second population consistedof larger, blown microcapsules containing the suspension fluid.Microcapsules of both populations may be suitable for use in accordancewith the invention, independently or in combination.

The microcapsules had very thin walls. They were self-fluidising and hada density of approximately 0.07 g/cm³. They were therefore suitable fortesting as products for delivery by the pulmonary route. The median sizeby volume distribution of these microcapsules was shown to be 10.7 μm byCoulter Counter sizing.

Using a multi-stage liquid impinger (MLSI) and a Dinkihaler, theaerodynamic diameter of the microcapsules was determined.

Three gelatin capsules were each filled with 10 mg of the microcapsules.Each stage of the MLSI was filled with 20 ml purified water, and the airflow set to 60 l/minute.

A single gelatin capsule was pierced at both ends and placed in theDinkihaler. The air flow was turned on for 30 seconds and then switchedoff.

The device and throat were each washed with 20 ml purified water. Eachstage was washed in a total of 25 ml purified water and the filter waswashed in 10 ml purified water. They were then assayed for protein bystandard methods.

The MLSI was washed thoroughly and prepared for a second run asdescribed above. 3 runs were carried out. Results are shown in thefollowing Table.

Percentage Accumulation Stage Run 1 Run 2 Run 3 Device 17.02 8.85 14.27Throat 22.62 11.57 18.08 1 (>13.4 μm) 4.78 2.66 5.31 2 (13.4-6.8 μm)14.58 18.30 12.99 3 (6.8-3.1 μm) 25.92 32.63 23.56 4 (3.1-1.7 μm) 7.9615.59 11.09 Filter (<1.7 μm) 1.38 4.64 7.58 Total Recovery (%) 94.3094.23 92.87

The respirable fractions (defined as particles below 6.8 μm) for runs1-3 were 33%, 53% and 42%, respectively. The results are alsorepresentative of the non-stabilised microcapsules, and suggest thatthis type of microcapsule is suitable for pulmonary delivery.

EXAMPLE 2

100 ml of diafiltered 20% w/w HSA solution containing 10 g ammoniumcarbonate was spray-dried on a Niro Mobile Minor spray-dryer. Thefollowing conditions were used:

Inlet temperature − 220° C. Atomisation pressure − 7.5 barg Feed rate −3.96 g/min Atomisation type − 2-fluid nozzle Liquid insert − 0.5 mm

5 g of the spray-dried microcapsules thus obtained were heat-stabilisedfor 55 minutes at 177° C. in a hot air oven. The stabilisedmicrocapsules were then deagglomerated with an equal mass of glucoseusing a Fritsch centrifugal pin mill.

The microcapsules were sized using a Coulter Counter fitted with a 100μm orifice tube which found that the volume median diameter of themicrocapsules was 10.1 μm. The echogenic properties were characterisedas described in Example 5 of WO 96/15814. The known microcapsules werefound to have echogenicities of around 26 VDU's; for the microcapsulesof this Example, containing a blowing agent, the corresponding value was69 VDU's.

What is claimed is:
 1. A composition comprising microcapsules, whereinsaid microcapsules have a wall thickness of no more than 500 nm, and abulk density of no more than 0.2 g.cm⁻³.
 2. The composition, accordingto claim 1, wherein the median size of said microcapsules is from 1 to20 μm.
 3. The composition, according to claim 1, wherein the wallthickness of said microcapsules is from 10 to 250 nm.
 4. Thecomposition, according to claim 3, wherein the wall thickness of saidmicrocapsules is from 100 to 150 nm.
 5. The composition, according toclaim 1, wherein the bulk density of said microcapsules is from 0.01 to0.15 g.cm⁻³.
 6. The composition, according to claim 5, wherein the bulkdensity of said microcapsules is from 0.04 to 0.1 g.cm⁻³.
 7. Thecomposition, according to claim 1, wherein the walls of saidmicrocapsules are comprised at least predominantly of albumin.
 8. Thecomposition, according to claim 1, obtainable by spray-drying awall-forming material, in combination with a blowing agent.
 9. Thecomposition, according to claim 1, wherein said microcapsules comprise atherapeutic agent.
 10. The composition, according to claim 9, whereinsaid microcapsules comprise a cotranscytosis factor.
 11. Thecomposition, according to claim 9, wherein said microcapsules comprisefibrinogen or thrombin.
 12. The composition, according to claim 9,wherein said microcapsules comprise an active agent selected from thegroup consisting of insulin, growth hormone, calcitonin, α-antitrypsin,FSH, α-interferon, β-interferon, heparin, Factor VIII, Factor IX,interleukins and blood coagulation factors.
 13. The composition,according to claim 9, which is soluble.
 14. An inhaler comprising aninhalable formulation of microcapsules wherein said microcapsules have awall thickness of no more than 500 nm, and a bulk density of no morethan 0.2 g.cm⁻² and wherein said microcapsules comprise a therapeuticagent.
 15. The inhaler according to claim 14, wherein the formulationcomprises the microcapsules as the sole or the predominant componentthereof.
 16. The composition, according to claim 1, which is insoluble.17. A method for pulmonary administration of a therapeutic agent whereinsaid method comprises the administration to the lungs of a compositionwhich comprises microcapsules having a wall thickness of no more than500 nm and a bulk density of no more than 0.2 g.cm⁻³, wherein saidmicrocapsules further comprise a therapeutic agent.
 18. The method,according to claim 17, wherein the median size of said microcapsules isfrom 1 to 20 μm.
 19. The method, according to claim 17, wherein the wallthickness of said microcapsules is from 10 to 250 nm.
 20. The method,according to claim 17, wherein the wall thickness of said microcapsulesis from 100 to 150 nm.
 21. The method, according to claim 17, whereinthe bulk density of said microcapsules is from 0.01 to 0.15 g.m⁻³. 22.The method, according to claim 17, wherein the bulk density of saidmicrocapsules is from 0.04 to 0.1 g.m⁻³.
 23. The method, according toclaim 17, wherein the walls of said microcapsules are comprised at leastpredominantly of albumin.
 24. The method, according to claim 17, whereinsaid microcapsules are obtainable by spray-drying a wall-formingmaterial, in combination with a blowing agent.
 25. The method, accordingto claim 17, wherein said microcapsules comprise a therapeutic agent.26. The method, according to claim 25, wherein said microcapsulescomprise a cotranscytosis factor.
 27. The method, according to claim 25,wherein said microcapsules comprise fibrinogen or thrombin.
 28. Themethod, according to claim 25, wherein said microcapsules contain anactive agent selected from the group consisting of insulin, growthhormone, calcitonin, α-antitrypsin, FSH, α-interferon, β-interferon,heparin, Factor VIII, Factor IX, interleukins, and blood coagulationfactors.
 29. The method, according to claim 17, wherein said compositionis soluble.
 30. The method, according to claim 17, wherein saidcomposition is insoluble.
 31. A method for diagnosis by ultrasound,wherein said method comprises administering to a patient in need of suchdiagnosis, a composition which comprises microcapsules having a wallthickness of no more than 500 nm and a bulk density of no more than 0.2g.cm⁻³.
 32. The method, according to claim 31, wherein the median sizeof said microcapsules is from 1 to 20 μm.
 33. The method, according toclaim 31, wherein the wall thickness of said microcapsules is from 10 to250 nm.
 34. The method, according to claim 31, wherein the wallthickness of said microcapsules is from 100 to 150 nm.
 35. The method,according to claim 31, wherein the bulk density of said microcapsules isfrom 0.01 to 0.15 g.m⁻³.
 36. The method, according to claim 31, whereinthe bulk density of said microcapsules is from 0.04 to 0.1 g.m⁻³. 37.The method, according to claim 31, wherein the walls of saidmicrocapsules are comprised at least predominantly of albumin.
 38. Themethod, according to claim 31, wherein said microcapsules are obtainableby spray-drying a wall-forming material, in combination with a blowingagent.
 39. A method for preparing microparticles, wherein said methodcomprises spray-drying wall-forming materials and wherein said methodfurther comprises inclusion of a blowing agent in the feedstock forspray-drying.
 40. The method, according to claim 39, wherein saidblowing agent is selected from the group consisting of ammonium acetate,ammonium hydroxide, ammonium carbonate, ammonium bicarbonate, aceticacid, formic acid, and hydrochloric acid.
 41. The method, according toclaim 39, wherein said wall-forming material is albumin.